The most common cause of this problem is that the truncated mails are using bare LFs for line breaks. Since most SMTP systems do not permit this, offending mails usually get truncated after about 1KB (this is a line limit enforced on many SMTP systems). This problem is particularly common with web scripts which generate HTML mails. If the truncation is occurring within Ability Mail Server, then there is an SMTP option available which should prevent this. Simply access the SMTP security settings and enable the option 'Convert Bare LFs into CRLF Pairs During Mail Transfer'. If any mail should then use bare LFs, they will be converted into the more correct CRLF pairs, and so avoiding any SMTP line limits.